current GTK+-2.22 bundle, can't find loaders.cache which is reside in lib\gdk-pixbuf-2.0\2.10.0\loaders\. 

Inside gdk-pixbuf-io.c
....
static gchar *
gdk_pixbuf_get_module_file (void)
{
  gchar *result = g_strdup (g_getenv ("GDK_PIXBUF_MODULE_FILE"));

  if (!result)
          result = g_build_filename (GDK_PIXBUF_LIBDIR, "gdk-pixbuf-2.0", GDK_PIXBUF_BINARY_VERSION, "loaders.cache", NULL);

  return result;
}
....

thus if GDK_PIXBUF_MODULE_FILE not set (default) will only look for GDK_PIXBUF_LIBDIR which is not valid for win32 platform